Support hash algorithm option.

[davidlehn]

• Add messageDigestAlgorithm option to API.
• Add support for SHA-256, SHA-384, and SHA-512 name variations to MessageDigests.
• Updates tests to handle hashAlgorithm option if present.

There may be a better way to handle the algorithm string normalization. This works for now. Node uses "sha384", WebCrypto uses "SHA-384", and the test suite uses "SHA384".

[codecov-commenter]

Codecov Report

Merging #78 (a127ad0) into add-signal-support (f52439f) will decrease coverage by 0.13%. The diff coverage is 90.90%.

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@@                  Coverage Diff                   @@
##           add-signal-support      #78      +/-   ##
======================================================
- Coverage               93.71%   93.59%   -0.13%     
======================================================
  Files                      10       10              
  Lines                     605      609       +4     
======================================================
+ Hits                      567      570       +3     
- Misses                     38       39       +1     

Files Changed	Coverage Δ
lib/index.js	56.86% <ø> (ø)
lib/MessageDigest.js	87.50% <75.00%> (-12.50%)	:arrow_down:
lib/MessageDigest-webcrypto.js	84.61% <100.00%> (+1.28%)	:arrow_up:
lib/URDNA2015.js	98.78% <100.00%> (ø)
lib/URDNA2015Sync.js	99.37% <100.00%> (ø)